1. Field of the Invention
The present invention relates to a fuel supply system of an internal combustion engine for automobiles, and more particularly to a fuel injector assembly including an alcohol sensor.
2. Description of the Prior Art
Gasolines are commonly used as the fuel for internal combustion engines for automobiles. The fuel is sprayed into an intake manifold and the mixture of air and fuel is supplied to the cylinders of the engine. The mixture is burned in the cylinders to convert the resulting heater into mechanical power by the pistons sliding in the cylinders. Thus, it is important to control the air to fuel ratio supplied to the cylinders at an optimum level best suited to the working conditions of the engine to ensure best performance thereof.
Gasolines used as fuels of internal combustion engines, however, are devided into various grades, and some of them include alcohols (methanol and/or ethanol) up to 15 percent. The inclusion of alcohols in gasolines substantially reduces the octane number of the fuel. Thus, if the air to fuel ratio is not modified according to the amount of alcohols added to the gasoline, the engine has the tendency to knock during starting. The tendency of knocking is especially manifest at the hot re-starting state of the engine.
Thus, Japanese laid-open utility model application No. No. 61-183435 proposes a fuel injector device for an internal combustion engine comprising a means for detecting the percentage of alcohols in the fuel. Utilizing the fact that the dielectric constant of alcohol is much greater than that of gasoline, the device of the Japanese utility model application determines the percentage of alcohol in the fuel by measuring the dielectric constant of the fuel. The device modifies the air to fuel ratio supplied to the engine in accordance with the detected percentage of alcohol in the fuel.
FIG. 1 shows a block diagram of a fuel injector device including an alcohol sensor. The device of FIG. 1 is similar to that disclosed in the above-mentioned Japanese utility model application. The fuel in the fuel tank 1 is pressurized by a fuel pump 2, and is supplied through a fuel pipe 2a to a fuel filter 3, and therefrom to a fuel delivery pipe 4 having nozzles 5. The fuel is injected from the valves of the nozzles 5 into an intake manifold coupled to the cylinders of the internal combustion engine. The pressure of the fuel is regulated by a fuel pressure regulator 6, and the fuel which is not injected into the manifold is returned through the fuel pipe 2a to the tank 1. The opening period of the valves of the nozzle 5 is controlled by the control unit 7 according to the measurements made by an alcohol sensor 8 disposed in the tank 1, so that the air to fuel ratio is adjusted to the optimum level.
The fuel injector of the above mentioned type, however, has the following two disadvantages:
The first disadvantage results from the delay between the time of measurement and that of injection. Namely, if the engine is started immediately after an amount of fuel is poured into the tank 1 in which a small amount of fuel remains which has an alcohol content different from that of the added fuel, then the fuel injected into the intake manifold immediately thereafter is that remaining in the fuel supply system between the tank 1 and the fuel delivery pipe 4, which fuel has an alcohol content different from that of the fuel in the tank 1. However, the sensor 8 detects the percentage of alcohol in the fuel in the tank 1. As the tubing from the tank 1 to the valves of nozzles 5 is relatively long, the air to fuel ratio is controlled to a wrong level, during an appreciable time period during which the old fuel in the fuel supply system is consumed, on the basis of the measurement of the alcohol content which is different from that of the fuel being injected. Thus, starting problems of the engine tend to occur.
The second disadvantage results from the position of the alcohol sensor in the tank 1. Namely, it is necessary to position the sensor 8 at the bottom of the tank 1 to ensure that the measurement of the alcohol content can be effected even when the fuel level lowers to be near to the bottom of the tank 1. In addition, water occasionally contained in the fuel tends to accumulate near the bottom portion of the tank. Thus, the measurement by the alcohol sensor situated at the bottom of the tank is adversely affected by the presence of this accumulating water which exhibits a very large dielectric constant. Consequently, the alcohol content of the fuel determined by the sensor tends to contain a large error due to the water which may be present in the tank. The air to fuel ratio may thus be controlled to a wrong level, and engine problems may ensue.